A range of strict new lockdown measures have been announced for the entire country, amid a surge in coronavirus cases.
Schools will stay closed until at least February 1st, with teaching moving online.
However, Leaving Cert students will be able to attend school three days a week from Monday, amid continuing plans for the traditional exams to happen in June.
All schools will be given 'autonomy' to decide how that will work in practice, Education Minister Norma Foley said.
There will also be measures in place for children with special needs so they can continue attending school.
Childcare services will generally be closed for the coming weeks, but they can remain open for vulnerable children and the children of essential workers.
Most construction will halt from Friday, although some essential projects such as housing and health will be allowed to continue.
Non-essential retail outlets are no longer allowed 'with immediate effect' (except for existing orders), but delivery services can continue.
Taoiseach Michael Martin confirms all schools will close from Monday for at least 3 weeks but Leaving Cert students will attend class for 3 days a week. Special education services can also remain open pic.twitter.com/36Zt2DHB1s
— Stephen Murphy (@StephenMNews) January 6, 2021
Passengers flying into Ireland, meanwhile, will need to prove they've tested negative for COVID-19 within three days of travelling.
It will apply to Britain and South Africa from Saturday, before later being rolled out to other countries.
Travelling without proof of a negative test result will be an offence, and potentially lead to a fine or imprisonment.
Taoiseach Micheál Martin said people 'simply must stay at home' unless they're involved in essential work.
He said the move to close schools was a 'difficult decision', but the spread of the virus means there's a need to stop as much mobility as possible for the next three weeks.
Tánaiste Leo Varadkar, meanwhile, warned we're facing a 'very dark January' with a risk of hospitals being overwhelmed.
He said therefore the message has to be to slow the virus and prevent its spread.
The Pandemic Unemployment Payment and Wage Subsidy schemes will remain in place until at least the end of March.